How to allow the iOS Google Calendar app to access events from Outlook or iCloud (2023).

GCalTools Calendar Tools:

Sheets2GCal (Sheets add-on)
Sheets2GCal is designed for advanced Google Calendar management using spreadsheets. Create or import events in a spreadsheet, edit them in the Sheet and export the changes to Google Calendar, or edit them in Google Calendar and import the changes back to Google Sheets.

More info: https://www.sheets2gcal.com/help
https://workspace.google.com/marketplace/app/sheets2gcal/137564231775

GCalToolkit (Desktop software)
Take control of Google Calendar with GCalToolkit Power Tools for osX, Windows and Linux: https://www.gcaltoolkit.com

GCalExtras (Calendar add-on)
GCalExtras integrates with Google Calendar to provide extra functionality such as saving/loading groups of calendars, mass copy/edit for a range of events, easy access to the event location text, and storing private notes associated with individual events.

More info: https://www.sheets2gcal.com/gcalextras/
https://workspace.google.com/marketplace/app/gcalextras/338335660766